This invention relates to a heat-sensitive record material and particularly to a heat-sensitive record marterial which is superior in retainability of the recorded images.
There has been well-known heat-sensitive record materials utilizing the colorforming reaction between a colorless or pale colored basic chromogenic material and an organic or inorganic color developer, in which the two colorforming materials are thermally brought into contact with each other to produce color images. These heat-sensitive record materials are relatively cheap and the recording machines are compact and easily maintained. Therefore, they have been used not only as a recording medium of facsimiles, various caliculator and the like, but also in the other various fields.
For example, in one case, the application as a label has been increased with the enlargement of the POS (point of sales) systematization in a retail store and the like.
When the POS system is induced in a super-market and the like, there are many cases in which the label is touched with water, lapping films, oil and the like and resultantly the recorded images on the heat-sensitive label are discolored. Therefore, it is required for the heat-sensitive record material to have good retainability of the recorded images, such as water-resistance, plasticizer-resistance, oil-resistance and the like.
As the methods for improving the retainability of the recorded images, there have been proposed such as the method of coating on the heat-sensitive recording layer a water-emulsion of a film-formable resin superior in chemical resistance (Japanese Laid-Open Patent Publication No. 128347 of 1979), the method of coating a water-soluble polymer such as polyvinylalcohol and the like (Japanese Laid-Open Utility Model Publication No. 125354 of 1981), and the method in which various kinds of agents for improving the image retainability are added in the heat-sensitive recording layer. However, in any cases, the other defects such as lowering the image density of the recorded images, lowering the whiteness of the heat-sensitive recording layer and the like are accompanied with the improvement. Satisfactory effects have not been obtained.
Furthermore, sufficient effects have not been obtained in wet-plasticizer-resistance which means water- and plasticizer-resistance.
Japanese Laid-Open Patent Publication No. 164579 of 1987 discloses the method in which diphenylsulfone derivatives having glycidyl group is added in the heat-sensitive recording layer. The retainability of the recorded images is improved by the addition of these compounds in the recording layer, but satisfactory qualities can not be obtained, because the whiteness of the recording layer is remarkably lowered by the occurrence of fogging.
Therefore, it is an object of the present invention to provide a heat-sensitive record material in which the retainability of the recorded images is remarkably improved in both of plasticizer-resistance and oil-resistance and the unrecorded white portion is stably maintained fogging free.
Further, it is an object of the present invention to provide a heat-sensitive record material being superior in image-retainability, in particular superior in plasticizer-resistance, water-resistance and wet-plasticizer resistance and also superior in image density, without lowering the whiteness of the unrecorded portion.